Police are following up various lines of enquiry in relation to a multiple vehicle crash in which six people died as they work to understand what caused the "harrowing" collision.

Three men were killed when they were thrown out of their car while a black cab driver and his two passengers, a man and woman, died after the vehicle was left on its side in Birmingham.

The scene of the collision.

A fourth man travelling in the car remains in a critical condition at the city's Queen Elizabeth Hospital.

Police said they are following various lines of investigation including the condition of the road when the crash happened at Belgrave and Lee Bank Middleway, near Edgbaston, at the junction of Bristol Road shortly after 1am on Saturday.

Superintendent Sean Phillips, from West Midlands Police, told a press conference : "It is way too early to speculate on the causes of the accident.

"It will take some time to unpick the scene and just understand exactly what's happened. It would be unfair for me to speculate at this time."

He confirmed the road had been gritted at 5pm the previous evening.

Asked about what speeds the vehicles were travelling and whether all of those involved were wearing seatbelts, Supt Phillips said those will be issues considered during the investigation.

The Ambulance Service, which sent five ambulances and three paramedics to the scene, said it was astonishing that a man and woman in the first car were able to escape with minor injuries despite "extensive damage" to their vehicle.

Three other cars collided as they tried to avoid the scene at the entrance to the underpass.

Of those people, two were taken to Heartlands Hospital with minor injuries.